On an aircraft, the ailerons are a control surface usually on the trailing edge of the wings. The ailerons are used to control roll by generating asymmetric wing lift. The ailerons are on the outside of the wings and operate oppositely (If one goes up, the other goes down).

Available seat miles (ASMs) is a measure of an airline flight's passenger carrying capacity. It is equal to the number of seats onboard an aircraft multiplied by the distance flown in miles. For example, a 100-seat aircraft flying 100 miles would result in 10,000 ASMs. Seats that are not available for sale to revenue-paying passengers (e.g., seats reserved for crew rest, etc.) are excluded from this calculation. The amount of ASMs flown by an airline during a specified period equals the sum of ASMs flown on all flights during the period.

Any moveable surface on an aircraft which controls its motion about one of the three principal axes. Ailerons, elevators, and the rudder are examples of control surfaces. In addition, other type of roll control surfaces are roll spoilers that dump lift on one wing or another (as opposed to ailerons), spoilerons (combined spoiler and aileron), and Flaperon (combined flap and aileron). Other combined controls include the ruddervator (combined elevator and rudder as on the "V" tailed Beech Model 35), Elevons combining elevator and ailerons and Flailavators which control pitch & roll as well as flaps in wing trailing edge control surfaces. Other subsidiary controls are pitch, roll, and rudder trim tabs and the adjustable pitch tailplane (the whole tailplane moves to trim the pitch axis).

The point at which the mass of the aircraft would be balanced if it were placed on that single point. The point changes depending on the loading of the aircraft: fuel, passengers, luggage, etc. Each aircraft has CG limits specified by its manufacturer. If the CG of the aircraft in its current configuration is outside of the specified limits, the aircraft may be unsafe to fly as the control surfaces will have insufficient authority to safely control the aircraft. For example, if the CG is behind the aft (rear) CG limit, the aircraft will tend to stall.

(CASM) – The unit operating cost of a carrier, also known as unit cost. The cost, expressed in cents to operate each seat mile offered. Determined by dividing operating costs by ASM (available seat miles).

The direction in which the aircraft is moving, not to be confused with the heading which is the direction the aircraft is pointing. The course and heading will usually differ because of crosswinds (see crab). The course is also different from the track which is properly the path over the ground that the aircraft has already flown (although course and track are sometimes used synonymously).

A crab is a maneuver used to counteract the drift of an aircraft caused by a crosswind. The pilot will offset the heading of the aircraft from the desired track by a calculated amount, and the aircraft's velocity combined with the wind through vector addition will give a net movement in the desired direction.

The angle that an aeroplane'swings make relative to the lateral axis (horizontal plane, when on level ground). A larger dihedral angle gives greater roll(lateral) stability at the cost of efficiency. If the wings angle upwards, it is called the dihedral angle. Downward angled wings are said to have an anhedral angle (increasingly referred to as negative dihedral).

A lighter-than-air craft that can be steered and propelled through the air. From the French word dirigeable meaning steerable. (This term is generally considered out-of-date. The modern term is airship.)

To rotate the pitch of the propeller blades until they are oriented directly into the airflow, providing the least air resistance and no thrust. The propeller is usually feathered when an engine fails.

Flaps (often confused with any of the other moveable surfaces) are used on wings to increase lift and/or increase drag as an aircraft flies progressively slower. Increased lift is usually achieved by increasing the wing area and the camber(shape) of the wing to a lesser extent. Increased drag will arise from increasing the area and camber but the greatest effect is achieved with large changes in camber.

A regulatory term describing a flight which may be conducted in atmospheric conditions where the pilot cannot fly the aircraft solely by reference to the natural horizon (e.g. in cloud and fog) and must fly only by reference to the aircraft instruments. Compare to Visual flight rules.

Structure that supports the aircraft's weight when it is not airborne, often including a shock absorbing mechanism. Wheels can be used for hard surfaces, skis or skids for ice or snow, and floats or pontoons if landing on the water. Some aircraft like flying boats do not require landing gear, since their hull can support them

The percentage of seats filled. Determined by dividing Revenue Passenger Miles by Available Seat Miles. Also a measure of the factor of loading on an aircraft, with comparison to gravity. Increases in steep turns and other abrupt manouvers. Given as a factor of gravity with 1g being the standardised acceleration at sea level on land.

A measurement of weight at a specific distance (moment arm) from a reference point. This measurement is used to verify the aircraft is within the Center of Gravity (CG) limits. Reference points vary between aircraft.

A Pitot tube is a measuring instrument used to measure fluid flow, and more specifically, used to determine airspeed on aircraft. The Pitot tube is named after its inventor, Henri Pitot, and was modified to its modern form by Henry Darcy.

A manoevre where an aeroplane pilot rolls the aircraft in one direction with the ailerons and yaws it in the opposite direction with the rudder. This results in the aircraft continuing to move forward but presenting a larger cross-section to the oncoming air - thereby creating drag and causing the aeroplane to lose altitude rapidly in a controlled manner.

A building at an airport where passengers transfer from ground transportation to the facilities that allow them to board aircraft; also, a building at an airport where freight is transferred from ground transportation to aircraft.

The path on the ground over which an aircraft has flown. Also used synonymously with course, the direction in which an aircraft is moving relative to the ground. Note that this is not necessarily the same as the aircraft's heading.

Thrust is the force upon a system (such as a rocket or jet engine) generated when that system expels or accelerates mass. The resultant thrust force is equal to and in the opposite direction of the expelled mass.

A small, powered aircraft which is extremely light(254 lbs or Less empty)and seats only one occupant. Ultralights are popular among hobbyists for being cost-effective and having lenient regulation. Ultralight type aircraft are generally heavier and can seat more than one occupant.

A regulatory term describing flights that are conducted only in conditions where the pilot can see the ground, or in some instances is flying in the free space above a cloud. Compare to Instrument flight rules.